1. Field of the Invention
The present invention relates to a screen input-type image display system, and in particular, to a screen input-type image display system having a capacitive coupling touch sensor which achieves a high resolution with a small number of electrodes.
2. Description of the Related Art
An image display device having a touch sensor (which is also called a touch panel) having a screen input function in which information is input through a touching operation (a contact and pressing operation; hereinafter simply referred to as “touch”) on a display screen with a stylus pen or the like is used in a mobile electronic device such as a PDA and a portable terminal, various home electronic devices, and stationary customer guidance terminals such as an automatic reception machine. For such an image display device having a touch input function, a method of detecting a change in resistance or a change in capacitance of the portion which is touched and a method of detecting a change of an amount of light of the portion blocked by the touch are known.
In such an image display device having a touch sensor, in order to improve the operability of the user and realize a new application (for example, inputting a figure), a detection function with a high resolution is desired.
For a detection method of high resolution, for example, JP 2006-179035 A discloses an input device. The input device disclosed in JP 2006-179035 A comprises a first group of switches for applying signals from a transmitter to detection electrodes in the vertical direction (X electrodes) and a second group of switches for extracting signals on the electrodes in the horizontal direction (Y electrodes) which are arranged in a two-dimensional matrix in the vertical and horizontal directions, and a signal detection circuit (AM modulation circuit). In this structure, a signal is input from a transmitter to one X electrode selected by the first group of switches, Y electrodes are sequentially selected one by one by the second group of switches in this state, and it is detected in the AM modulation circuit whether or not an increase of the electrostatic capacity occurs in the X electrodes. The X electrodes to which the signal from the transmitter is applied are sequentially selected. A change of the electrostatic capacity at a touched location on the screen on which the information is input is detected by repeating these operations.